alternator not charging - (tacho draining voltage) FIXED

[mcerbm]

K-series, VHPD Superlight R

I had an issue with my alternator where the battery died (unfortunately when the car was being run in from an engine build, which gave me a red herring thinking there was issues elsewhere).

To get the car up and running I have a 12V feed from the ignition to the alternator to alow  it to get a signal to charge. This got me running for the season. But now I want to find the problem with the original wiring.

The original wiring was only giving 10Volts. This is on the brown wire with yellow stripe. I have chased the 10V from the alternator end of the spade, through the engine loom plug and to the back of the tacho. Its 10V coming out and 12V going in through the fused supply (green cable).

Any suggestions? What type of plug is it onto the tacho so I can maybe open up and order new crimped sockets to try and replace. Or is the tacho goosed internally? The tacho works fine.

[Jonathan Kay]

What type of alternator?

How many wires of what colour and size are currently connected to it?

What's the battery voltage at rest, minimum during cranking and at 3,000 rpm?

Does the ignition warning light come on with the ignition and go off when the engine's running?

Jonathan

[Jonathan Kay]

Do you already have an appropriate Assembly Guide? Let me know if you'd like one. The "standard" wiring colours might also help.

What type of plug is it onto the tacho so I can maybe open up and order new crimped sockets to try and replace.

I discovered to my surprise (and cost) that there are (at least) two different types of multiway plugs into "ordinary" analogue Caterham tachometers.

Jonathan

[revilla]

If you have an LED alternator warning light, there will be a voltage drop of around 2.2V across the LED, so you should only expect to see close to 10V at the alternator. I've seen a few cases now where an LED must isn't supplying enough current to kick start the alternator and a parallel power resistor or bulb is required.

[mcerbm]

Thanks for the quick replies. I hadn't seen the colour code chart before, thats very useful! I have the assembly guides and wiring diagrams for my car thanks Jonathan.

The whole ordeal has been a bit of a learning curve for me really. I thought the NY wire was just a warning light, I didnt know it had to also feed the alternator 12V to tell the alternator to provide charge. In the process of finding this out I jumped to a new alternator (had a race event in two days at the time!). So I swapped out my EU2 standard magnetti Marelli alternator for a WOSP alternator. It only has the big charging post for the battery and a spade for the warning light (12V ignition feed).

The car has been running on a separate wire from igniton to alternator to provide the feed. I haven't had the original wiring on the alternator for a few months (well since I discovered the problem).

The car isnt currently running at the moment as I'm doing a few wiring jobs as the scuttle is off. But checking with the ignition on the NY wire was getting 10V but it wasnt connected to the alternator at the time. I re-attached it to the spade on the alternator and the red alternator warning light came on in the tacho. The voltage jumped to 5.6V!

 

[mcerbm]

I should say that I am measuring this by placing a multimeter needle probe into the cable entry part of the tacho plug so I can see what the plug is getting.

so far its:

12V in by green supply wire

10V out if NY wire not connected to anything (broken circuit)

5.6V if NY connected to alternator and tacho warning light on

[mcerbm]

This is the alternator if it helps

WOSP K-series 65A race alternator part# LMA226

[Jonathan Kay]

WOSP K-series 65A race alternator part# LMA226

WOSP's information doesn't seem to be consistent:

1. Here it only has two connections "B+" and "Lamp" (and by implication doesn't need another exciter feed).
2. Here it has "B+/IG/L/S ".

How many connectors does yours have?

Previous discussion of this issue, and where to get the proprietary connector.

Jonathan

PS: I've emailed WOSP asking for clarification despite their website stating "We are unable to deal with the public directly. Sorry!".

[mcerbm]

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It only has B+ and the lamp. 

[mcerbm]

Thanks for the connector heads up, I have just been using a heat protected spade. Ordered now!

[mcerbm]

If its an issue internal in the tacho. Would I be able to bridge the input 12v wire (green) with the "lamp" (Brown / yellow) wire by soldering a link just behind the tacho input plug?

That way whatever is happening inside the tacho pulling down the voltage wouldn't matter?

[Jonathan Kay]

I'm confused. 

Which alternator do you want on the car when it's all sorted?

Do you also want to test the other alternator to know that it's charging and otherwise behaving normally?

Jonathan

[mcerbm]

Jonathan it’s the WOSP that’s installed at the moment and it’s the one I want to keep. The photo on the scales was prior to fitting. I do have the old EU2 alternator still in the for sale section. But being heavier I don’t want to refit.

ideally I’m looking to decommission the original wiring and stop using my extra 12v feed to the alternator I had wired in last season.

I know from testing last year that the WOSP doesn’t charge without the 12V lamp feed  

it looks like my Tacho is the source of the problems. I would like to bridge the 12v in feed with the lamp circuit at the tacho plug. But now sure if that has any unforeseen circumstances. 

[Jonathan Kay]

Thanks.

Do you know if the current lamp is an LED, as in post #4? If that involves removing the tachometer please could you take a photo of the back and the connector.

How does the warning lamp behave?

What's the battery voltage at rest, minimum during charging and at 3,000 rpm?

Jonathan

[mcerbm]

This is my tacho here, it looks like it is an LED for the warning circuit

https://caterhamparts.co.uk/gauges/219-tacho-0-8000-rpm-052000-to-082001.html?search_query=tacho&results=15

The car isnt running just now, should be later in the week so I can check. From memory when first diagnosing the problem the bulb circuit attached (WOSP alternator) = 14.4V at idle. With the bulb circuit removed it was 11.5V. That was after my new 12V feed run from ignition to alternator.

With the original wiring (and OEM alternator) I didnt manage to get the alternator charging at all. 11.5V at idle, and it wasnt charging when driving either. The car came to a halt as the battery died. That led to the new WOSP alternator, it also didnt charge until a new circuit was put in from ignition to alternator "Bulb".

[mcerbm]

 I've seen a few cases now where an LED must isn't supplying enough current to kick start the alternator and a parallel power resistor or bulb is required.

This I presume is whats happening to me but there is maybe a fault / corrosion inside the tacho that is making it worse (10V with no warning light on, 5.6V with warning light on).

How do I install a parallel power resistor? Is that the same thinking as my suggestion to bridge the 12V feed with the "bulb" wire to the alternator but done properly? Caterham has my tacho out of stock, and ideally i'm after a work around rather than a new tacho.

[revilla]

OK, let me just check I'm understanding this correctly ...

• You are measuring the voltage on the alternator end of the Brown/Yellow wire every time?
• You are using a multimeter to measure the voltage between this wire and a known good earth every time, e.g. you connect the red multimeter lead to this wire and the black lead to say the battery negative terminal?
• When this is not connected to the alternator, it reads around 10V relative to earth?
• When this wire is connected to the alternator, it reads around 5.6V relative to earth?

If this is all correct, it's not the tacho that is "draining voltage" (remember the other end of the wire is connected to the tacho all the time. It's more that that tacho (i.e. the warning LED inside it and the series resistor which it will inevitably has as LED's won't want 12V across them, they generally run at about 2.2V) is not feeding enough current into the alternator to pull the voltage up any higher than 5.6V. If you measure the voltage on the alternator terminal rather than on the wire, I would expect to to be close to zero with the wire disconnected; this then jumps up to 5.6V when you feed it with exciter current through the warning LED and internal resistor. This may not be enough, we need to look at feeding more current. To be honest I'm not sure what voltage to expect here when not charging. I can check it out on my car but it might vary between alternator designs.

In a way, yes fitting a high powered resistor in parallel is the same as just taking that wire straight to the battery, but doing it that way you lose the warning light functionality; what you need is a way of keeping the warning light but feeing the alternator with more current to get it going (assuming of course that this is the problem).

This is what I would do to test this: You need a 12V bulb, somewhere around 2W to 4W, with two lengths of wire attached. Connect one end to the positive battery terminal. Connect the other end to the Brown/Yellow wire at the alternator (i.e. connect both one of the test bulb wires and the original wire to the alternator at the same time). You should find the bulb lights up straight away. When you turn the ignition on, the warning light on the dash should come on too. It may be a bit dim, depending on the bulb wattage. When you start the engine, hopefully both will then go out, and the alternator will be charging. The additional current from the bulb should be enough to start it up.

If this all works, you need to wire up something a bit more permanent, but instead of connecting to the positive battery terminal, connect the bulb into a wire that is supplied through the ignition switch, so the bulb only comes on when you turn the key on. You can either use a small bulb holder, or just replace it with a resistor of an appropriate resistance and power rating - we can worry about the details once we know what we're dealing with.

If not, we need a rethink - but to be honest the external circuit for an alternator is so simple (usually earth to the block, output to the battery, and the warning) that there isn't much else to go wrong, other than something internal to the alternator and you've swapped that out already. None of the other earth points, e.g. under the dash, are at all relevant. And if the starter motor will crank the engine, you know the earth to the block is good.

If you are stringing makeshift wires around the alternator and battery be careful as they will be un-fused lives, so make sure the test bulb is well insulated and make a decent to of terminating the wires so they can't short to anything.

If you want me to make up a safe test lead for you, with a ring terminal for the battery end and a spade terminal on the other, with a spur to plug the original wire into to keep it all safe, just let me have your address. I've got all the bits in my garage and it will only take five or ten minutes in an evening - and I'm happy to plug it into my own car to make sure nothing goes bang before posting it!

Andrew

[mcerbm]

Revilla thanks for a thoroughly comprehensive response, much appreciate your time looking at this. To answer your initial bullets

• You are measuring the voltage on the alternator end of the Brown/Yellow wire every time?

I was using a multimeter with needle probe to insert into the tacho connector where the Brown Yellow wire enters. I will repeat the test at the alternator end tonight.

• You are using a multimeter to measure the voltage between this wire and a known good earth every time, e.g. you connect the red multimeter lead to this wire and the black lead to say the battery negative terminal?

Yes back to battery earth each time

• When this is not connected to the alternator, it reads around 10V relative to earth?

Yes

• When this wire is connected to the alternator, it reads around 5.6V relative to earth?

Yes

 

I have a caterham warning light bulb, I think it is just a traditional bulb rather than a LED I could use for your test. Its this one:

https://caterhamparts.co.uk/other/986-warning-light-red.html?search_query=warning+light&results=175

I think what you are suggesting is what I have been using as a work around but with no bulb. I have a individual wire run from my aero ignition switch with an inline fuse that goes to the alternator bulb spade. I ran the car with this for approx 9 months. With the original bulb light wiring disconnected. Ideally I would like to get the original wiring working again (with no additional lines). I will get some results up later in the week. Thanks for the offer of making test cables, I have made a few already to help with this. I will make a wire extension for the alternator bulb spade so I dont burn my hands on the exhaust and also extend the original wiring and bodge job wiring so that I can the car running and switch between each alternator bulb feed and try each on its own and in combination with car off / running etc and post the results.

[mcerbm]

Revilla, I have some tests from last night.

Battery voltage = 12.15V, all checks done at alternator end of wire or on spade connection of alternator

---- Not connected to alternator spade (Open circuit)

Brown yellow original wire = 10.0V

"bodge" Fused ignition live = 11.9V

Fused ignition live with bulb = 11.9V

------ Connected to alternator spade and measured at spade

Brown yellow original wire = 7.5V

"bodge" Fused ignition live  = 11.7V (humming heard from alternator)

Fused ignition live with bulb  = 0.71V

----- 

Brown yellow wire + "bodge" Fused ignition live both connected to alternator spade = 11.9V

Brown yellow wire + Fused ignition live with bulb both connected to alternator spade = 0.72V

-----

I dont have the car ready for starting and doing running tests yet. BUt if you let me know what else needs done to problem solve I can hopefully do it soon. Thanks for teh continuing assistance!

[revilla]

Hi,

First thing I would say is that most of those voltages look reasonable except for the 7.5V with the original wire connected. Are you sure about that one? It would imply that the original circuit is feeding a lot more current that a bulb.

Secondly, it's much more about the current flowing that the voltage; the voltage you will see at that terminal will depend rather a lot on the internal circuitry, and since there are diodes in there which are nonlinear and an active regulator, the relationship between voltage and current will not be a simple one. The open circuit voltages with no current flowing don't really tell a lot. I suspect the voltages of 0.7-ish suggest you're measuring the forward voltage of the internal diodes plus a bit of voltage across a winding.

The first thing is, I would stop using that "bodge wire". Humming from the alternator does not sound at all normal! In fact given that it's all DC, the only thing I can think of that would make it hum would be the internal regulator and protection circuitry cycling something on and off rapidly because it's not happy. It sounds like a pretty low impedance to ground at that terminal and it will rely on the resistance of the bulb or whatever feeding it to limit the current; as I say it's more about the current than the voltage and by strapping it to the positive battery terminal you're probably risking frying something like a diode quite quickly.

You could if you want measure the current flowing using the original Brown/Yellow wire and through the bulb; in each case, leave the wire disconnected from the alternator and with the multimeter in current mode, connect the probes one to the relevant wire and one to the alternator. Don't even try this with the "bodge wire", I suspect it would cost you the price of a new multimeter, or the price of a new fuse if you're lucky.

I think the best thing to do next would just be to wire the bulb up in place of, or in parallel with the existing wiring and wait until you are in a position to test it with the engine running. Hopefully all will be OK.

[mcerbm]

Hi revilla,

I got this response from WOSP :

Me:

‘’I purchased WOSP alternator part# LMA226 last year. The alternator only has B+ and lamp as connections. What is the minimum voltage (or current) that needs supplied via the lamp circuit to allow the alternator to provide voltage?"

WOSP:

The alternator pulls 3.5amps via the lamp circuit to excite the alternator. Ideally a 3W bulb and no more than 5W. If the customer is running an LED bulb it may provide too much resistance to provide the alternator with current to excite therefore it may need bypassing by a resistor. We supply these if necessary.

 

[revilla]

Well that pretty much backs up what we thought. However the numbers don't stack up; a 3W-5W bulb (which is pretty close to my suggested 2W-4W) is going to allow the alternator to pull at most about 0.25-0.41A continuous ... Are you sure there's not a decimal place error and the alternator wants to pull 0.35A? That would make a lot more sense.

[revilla]

And "no more than 5W" definitely suggests you shouldn't be shorting the lamp terminal straight to the battery.

[mcerbm]

I should have the car running tomorrow for testing and give back results.

I think I know which way to go. If I re-instate the original wiring and its an internal fault in the tacho meaning I cant use it to allow the alternator to charge then I will use a new warning light on the dash and feed it 12V (teed off the tacho 12V supply), then off down the original brown yellow wire which will be disconnected from the tacho.

I actually had a low oil pressure light in the dash which is now redundant which I will use. I was never quite happy with its viability as its partly hidden by the steering wheel so I moved the low oil warning light to my tacho using its inbuilt shift light. Its a bigger brighter more prominent light. shift lights are taken car of by a ACES unit so it was no loss.

I will update once tested. Bodge wiring and its cable tied route through my engine bay will then be removed.

[mudguard]

I've also just had the red light of doom, ironically enough on my first run out to test my new Toyos.

It hasn't ever done this during my ownership (20 months). Initially, everything was normal, tacho LED extinguished immediately on engine start. About 15 minutes in, towards the end of the warm up, it suddenly came on. 

Fortunately wasn't too far from home so went straight back. Checked that alternator belt is intact, started measuring voltages and my multimeter promptly blew up (and yes it was set correctly!) so a new one is on the way.

The plug with the yellow+brown wire is intact and sound. The problem doesn't clear with a restart. Starter is turning the engine over really well, so I don't think I have a battery problem. 

So I think the next step is to determine whether it's the insufficient-exciter-current problem or the failed-alternator problem. So I'd like to run a temporary test wire from the battery +ve to the yellow+brown at the alternator. But - newbie question - how do I physically achieve that temporary connection at the alternator end? Preferably without damaging the loom?